Recording method for magnetic recording medium, recording device for magnetic recording medium and magnetic recording medium

ABSTRACT

After a DC erasing is performed in a direction by permanent magnets on a servo signal recording part, servo signals are recorded in the signal recording area of the servo signal recording part by a magnetic field in the direction opposite to that of the DC erasing. Thus, in a recording method for a magnetic recording medium having a data signal recording part and the servo signal recording part on a magnetic layer, accurate servo signals can be recorded and reproduced even on the medium having the magnetic layer of 0.13 μm or smaller.

The subject matter of application Ser. No. 10/985,815 is incorporatedherein by reference. The present application is a Divisional of U.S.application Ser. No. 10/985,815, filed Nov. 10, 2004, now U.S. Pat. No.7,224,544, which claims priority to Japanese Patent Application No.JP2003-379620, filed Nov. 10, 2003 and Japanese Patent Application No.JP2004-155417, filed May 26, 2004. The present application claimspriority to these previously filed applications.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording method for a magneticrecording medium, a recording device for a magnetic recording medium anda magnetic recording medium.

2. Description of the Related Art

In recent years, a demand for a high-density recording has beenincreased. A property suitable for the high-density recording is alsorequested for a magnetic recording medium as a recording medium ofinformation. Accordingly, various kinds of improvements are performed onthe magnetic recording medium.

For instance, in a linear magnetic tape used for the recording medium ofa computer or the like, recording tracks for recording the informationin the longitudinal direction of the tape are provided. Distancesbetween the recording tracks are narrowed to improve a track recordingdensity and achieve the high-density recording.

However, when a magnetic head records and reproduces the information,the magnetic head jumps over an adjacent data recording track to move inthe direction of width of the tape and access a prescribed recordingtrack. Accordingly, when the distances between the recording tracks aretoo small, interference is generated between the recording tracks. Thus,the information cannot be precisely recorded and reproduced.

Thus, media having servo signals respectively between the recordingtracks of the magnetic tape is developed. In the above-described media,servo signal parts are formed respectively between the recording tracks.Accordingly, the interference between the recording tracks uponrecording and reproducing the information and the dislocation(off-track) of a reproducing head from the recording track can beprevented.

Thus, the track recording density can be more improved to achieve thehigh-density recording. Further, in the media in which these servosignals are recorded, the interference between the recording tracks uponrecording and reproducing the information can be prevented, so thatoutput characteristics or overwrite characteristics are improved.

The magnetic recording medium and a recording method for recording theservo signal are proposed in, for instance, Japanese Patent No. 3116531.Further, as DC (direct current) erasing means of the present invention,a magnetic head described in, for instance, Japanese Patent ApplicationLaid-Open No. hei 10-124820, Japanese Patent Application Laid-Open No.hei 10-172109, Japanese Patent Application Laid-Open No. hei 9-282608,and Japanese Patent Application Laid-Open No hei 7-37225 can be used.

Further, a metallic thin film type magnetic recording medium and amethod for producing a metallic thin film type magnetic recording mediumare proposed in, for instance, Japanese Patent Application Laid-Open No.2003-296919, Japanese Patent Application Laid-Open No. 2003-85742,Japanese Patent Application Laid-Open No. 2003-45018, Japanese PatentApplication Laid-Open No. 2003-6851, Japanese Patent ApplicationLaid-Open No. 2003-346329, Japanese Patent Application Laid-Open No.2002-367135, and Japanese Patent Application Laid-Open No. 2002-245611.

In the magnetic tape having the high recording density, the servosignals are very important, so that all the servo signals need to have ahigh quality. Particularly, when the output of the servo signal is low,the position of the recording and reproducing head cannot be properlycontrolled. In an extreme case, a servo head undesirably misses theservo signal. Further, when time is not precisely recorded (jitter islarge), the same problem may be possibly generated.

In a tape for storage having a higher recording density than that of aconventional tape, the thickness of a magnetic layer is apt to bereduced. In a conventional particulate type recording medium, when thethickness of a magnetic layer is about 0.15 μm to 0.20 μm, a sufficientoutput of a servo signal has been obtained.

In a conventional servo signal recording system, only servo signal partsare magnetized in the directions as shown arrow marks as illustrated inFIG. 9A and no signal parts are not magnetized. Accordingly, there isnot a boundary area in which a magnetized direction is completelyinverted, so that obtained signals are low in S/N ratio as shown in FIG.9B.

Therefore, the media in which the thickness of the magnetic layer issmaller than 0.13 μm due to the high density recording can obtain onlyabout half an output by the conventional servo signal recording system,which causes a great trouble for an accurate reproduction of the servosignals.

Further, what is called an evaporated tape in which a metallic thin filmis directly formed on a base film also has an important problem toimprove a servo output.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems of aprior art and to record and reproduce an accurate servo signal in amagnetic recording medium having a magnetic layer having the thicknessof 0.13 μm or smaller.

In order to achieve the above-described object, the inventors of thepresent invention eagerly studied. Then, they obtained a knowledge thatthe directions of magnetization recorded on servo signal recording partswere different between signal recording sections and no signal recordingsections so that a high reproduced output and a high S/N ratio could beobtained when a servo signal was reproduced.

Specifically, the present invention relates to a recording method for amagnetic recording medium having a data signal recording part and aservo signal recording part on a magnetic layer. The recording methodcomprises the steps of: DC (direct current) erasing the servo signalrecording part; and then recording a servo signal in the signalrecording area of the servo signal recording part by a magnetic field inthe direction opposite to that of the DC erasing.

Further, the DC erasing is also performed to the data signal recordingpart.

Further, the DC erasing is performed by magnetizing the magnetic layerby a DC magnetic field.

Further, the present invention relates to a recording device for amagnetic recording medium having a data signal recording part and aservo signal recording part on a magnetic layer. The recording devicecomprises: a DC erasing means for DC erasing the servo signal recordingpart; and a servo signal recording means for recording a servo signal inthe signal recording area of the servo signal recording part by amagnetic field in the direction opposite to that of the DC erasing.

The DC erasing means also DC erases the data signal recording part.

Further, the present invention relates to a magnetic recording mediumhaving a data signal recording part and a servo signal recording part ona magnetic layer. In the magnetic recording medium, a DC erasing isperformed to the servo signal recording part and then a servo signal isrecorded in the signal recording area of the servo signal recording partby a magnetic field in the direction opposite to that of the DC erasing.

Further, the DC erasing is also performed to the data signal recordingpart.

Further, a magnetic film on which the servo signal is recorded is madeof a metallic thin film.

Further, the DC erasing is performed by magnetizing the magnetic layerby a DC magnetic field.

In each of areas obtained by dividing the magnetic layer into aplurality of parts in the direction of width, the servo signal recordingpart and the data signal recording part are alternately formed. In theservo signal recording part, a plurality of servo signals having a firstprescribed oblique direction with respect to an axis perpendicular to alongitudinal direction and a plurality of servo signals having a secondoblique direction different from the first oblique direction arealternately recorded.

According to the present invention, the magnetizing direction of thesignal recording area by recording the servo signals and the magnetizingdirection of a non-signal area by DC erasing the servo signal recordingpart are opposite to each other. Accordingly, a boundary area in whichthe magnetizing direction is completely inverted is formed. Thus, aleakage flux is increased more than a conventional method so that a highreproduced output and a high S/N ratio can be obtained upon reproducingthe servo signal and the servo signal can be more accurately and rapidlyreproduced from the magnetic recording medium on which a high-densityrecording is carried out.

Accordingly, a jitter and a defect are reduced and a highly accuratetracking operation can be performed. As a result, a track pitch of themagnetic recording medium can be reduced to increase a recordingdensity.

The present invention can extremely advantageously obtain theabove-described effects in the magnetic recording medium having amagnetic layer of 0.03 μm to 0.13 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view of a servo signal recording device accordingto one embodiment of the present invention.

FIG. 2 is an explanatory view showing one example of a recording patternof a magnetic tape according to the present invention.

FIG. 3 is an explanatory view showing one example of a tape magnetizingdirection in one embodiment of the present invention.

FIG. 4 shows a recording method in the embodiment of the presentinvention. FIG. 4A is an explanatory view showing a tape magnetizingdirection.

FIG. 4B is a signal waveform view.

FIG. 5 is an explanatory view showing one example of a method forevaluating the quality of the servo signal.

FIG. 6 is a conceptual view of a servo signal recording device accordingto another embodiment of the present invention.

FIG. 7 is an explanatory view showing one example of a tape magnetizingdirection in another embodiment of the present invention.

FIG. 8 is an explanatory view showing one example of a tape magnetizingdirection in another embodiment of the present invention.

FIG. 9 shows a conventional recording method. FIG. 9A is an explanatoryview showing a tape magnetizing direction. FIG. 9B is a signal waveformview.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described indetail by referring to the drawings. FIG. 1 shows one example of a servosignal recording device according to the present invention and is aconceptual view of a device for recording a servo signal S on a magnetictape T.

In FIG. 1, reference numeral 11 designates a recording head unit (servosignal recording means) in which a magnetic head (a recording head) forrecording the servo signal S is disposed. Reference numeral 12designates a DC (direct current) erasing unit (DC erasing means) having,for instance, three DC magnets for polarizing the magnetic tape T beforea recording operation. 13 designates a reproducing head unit in which amagnetic head (a reproducing head) for reproducing the servo signal S isdisposed.

Further, the servo signal recording device has conveying means forlongitudinally conveying the magnetic tape T from a tape taking out part14 to a tape winding part 15.

FIG. 2 shows one example of a recording pattern of a magnetic recordingmedium for independently recording data signals and servo signals. InFIG. 2, servo band parts (Servo Bands 0 to 4) on which the servo signalsS are recorded have a plurality of recording tracks Ta (data band parts;Data Bands 0 to 3) extending in the longitudinal direction in thedirection of width. Servo tracks Tr are formed by sandwiching each ofthe recording tracks Ta in the direction of width in between them toarrange and record the servo signals S having a prescribed pattern inthe longitudinal direction.

Accordingly, when the magnetic tape T has, for instance, four recordingtracks Ta, five servo tracks Tr are formed. In the illustrated example,five servo signals S5 a inclined at a prescribed angle, five servosignals S5 b inclined in opposite directions thereto at the same angle,four servo signals 4 a inclined at a prescribed angle and four servosignals S4 b inclined at the same angle in opposite directions theretoare considered to be one pattern. This pattern is repeated to form theservo tracks Tr.

As a base material of the magnetic recording medium used for thisembodiment, film type materials such as polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polyamide resin (alamide), etc.are used. The present invention is applied to what is called a two-layerparticulate type recording medium including a non-magnetic layer and amagnetic layer formed on the base. Further, as described below, thepresent invention may be applied to what is called an evaporated tape inwhich a magnetic layer such as Co, Ni is formed on the base by a vacuumevaporation method.

The thickness of the magnetic layer in the two-layer particulate typerecording medium of this embodiment is desirably located within a rangeof 0.03 μm to 0.13 μm. When the thickness of the magnetic layer is notlarger than 0.03 μm, the output of the servo signal cannot besufficiently obtained due to the small thickness of the magnetic layer.When the thickness of the magnetic layer is not smaller than 0.13 μm,when the servo signal is recorded by a recording system of the presentinvention, a reproducing signal becomes too large. Thus, theamplification of the servo signal may be possibly saturated so that theservo signal cannot be accurately reproduced.

Further, the thickness of the non-magnetic layer is desirably locatedwithin a range of 0.5 μm to 2.5 μm. When the thickness of thenon-magnetic layer is not larger than 0.5 μm, rough protrusions of abase film cannot be covered to cause a missing pulse (what is called adefect) to be generated.

The magnetic resistance of the magnetic tape of the present invention isdesirably located within a range of 144 to 220 kA/m. When the magneticresistance is not higher than 144 kA/m, the output of a data signalcannot be sufficiently obtained. Thus, the magnetic tape is not suitablefor a mass storage medium.

As a recording method for magnetization, a recording method as shown,for instance, in FIG. 3 may be exemplified. In FIG. 3, reference numeral21 designates a recording head in the head unit 11 shown in FIG. 1. 22 ato 22 c designate permanent magnets in the DC erasing unit 12 shown inFIG. 1.

The DC erasing is firstly performed using a magnetic field in thedirection opposite to that of a magnetic field for recording the servosignal by using the permanent magnets 22 a to 22 c. Then, the servosignal is recorded by using the magnetic field in the opposite directionto that of the DC erasing by the recording head 21.

An arrow mark 31 in FIG. 3 shows a conveying direction of the magnetictape T, an arrow mark 32 shows a DC magnetizing direction by DC erasingand an arrow mark 33 shows a magnetizing direction by recording,respectively.

As the above-described methods for DC erasing, a method of using apermanent magnet, a method of using a coil and a magnetic head or thelike may be exemplified. The permanent magnet to be used has a residualmagnetic flux density of 1.0 tesla or higher and a coercive force of10000 oersted (796 kA/m) or higher so as not to locally generateunevenness in erasing due to a magnetic flux. As the permanent magnethaving the above-described characteristics, a rare earth magnetincluding materials such as Nd—Fe—B (neodymium-iron-boron), Sm—Co(samarium-cobalt), or the like as main components may be employed. Thesepermanent magnets may be plated with Ni and used.

When the magnets are arranged, it is important to allow the magneticfield opposite to the magnetic field for recording the servo signal tocome near to the tape. When the magnetic field should be written in thesame direction, the signal would be hardly outputted. Since the outputof the servo signal is greatly associated with the quality (defect,jitter) of the servo signal, the output of the servo signal is desirablylocated within a range of 80 to 180 mV. When the output of the servosignal is not higher than 80 mV, a servo defect is too large so that acorrect position cannot be traced by the head. To control the output ofthe servo signal, a distance between the permanent magnets 22 a to 22 cand the magnetic tape T is changed so that the intensity of the magneticfield due to the DC erasing can be controlled.

The servo signal is recorded as described above. Accordingly, themagnetizing direction (shown by the arrow mark 32) by DC erasing in anon-signal area is opposite to the magnetizing direction (shown by thearrow mark 33) by recording the signal in a signal recording area, asshown in FIG. 4A.

Therefore, a boundary area in which the magnetizing direction iscompletely inverted is formed. Thus, a leakage flux is more increasedthan that of a conventional method and a high reproduced output and ahigh S/N ratio can be obtained upon reproducing the servo signal asshown in FIG. 4B.

EXAMPLE 1

Now, the present invention will be described on the basis of specificexperimental results. In a two-layer particulate type media of thisexample, on a base film made of polyester terephthalate, a non-magneticlayer composed of α-Fe₂O₃ and polyurethane is formed and a magneticlayer made of Co—Y—Fe ferromagnetic material and polyurethane is formedthereon as shown in FIG. 3.

(Coating Material for Lower layer) α-Fe₂O₃ 100 parts by weight vinylchloride copolymer (MR-110 produced by 10 parts by weight Nippon ZeonCo., Ltd.) polyurethane resin (UR-8300 produced by 10 parts by weightToyobo Co., Ltd.) carbon black 20 parts by weight butyl stearate 2 partsby weight stearic acid 1 part by weight methyl ethyl ketone 100 parts byweight toluene 50 parts by weight cyclohexanone 100 parts by weight

The above-described composition was kneaded by an extruder, premixed,then, dispersed by a sand mill, and processed by a filter with afiltration accuracy of 1 μm to prepare a coating material for a lowerlayer.

(Coating Material for Upper Layer) Co-Y-Fe ferromagnetic material 100parts by weight vinyl chloride copolymer (MR-110 produced by 10 parts byweight Nippon Zeon Co., Ltd.) polyurethane resin (UR-8200 produced by 10parts by weight Toyobo Co., Ltd.) carbon black 5 parts by weight alumina10 parts by weight butyl stearate 2 parts by weight stearic acid 1 partby weight methyl ethyl ketone 100 parts by weight toluene 50 parts byweight cyclohexanone 100 parts by weight

The above-described composition was kneaded by an extruder, premixed,then, dispersed by a sand mill, and processed by a filter with afiltration accuracy of 1 μm to prepare a coating material for an upperlayer.

The coating material for the upper layer was filled with a curing agent(Coronate L produced by Nippon Polyurethane Industry Co., Ltd.) of 4parts by weight and the coating material for the lower layer was filledwith a curing agent of 2 parts by weight. Then, two layers were appliedon the base film at the same time. After that, a pancake with the widthof 12.650 mm was obtained via processes of calendering, curing andcutting. The thickness of the magnetic layer of the Example was locatedwithin a range of 0.08 to 0.15 μm.

(Example of Recording of Servo Signal)

As the permanent magnet for DC erasing, three Nd—Fe—B magnets having themagnetic resistance of 1038 kA/m and the residual magnetic flux densityof 1.375 T were used to direct the magnetic field opposite to that forrecording the servo signal to the magnetic tape. In this Example, an Spole was directed to the magnetic tape. A distance from the magnetictape, the output of the servo signal and the quality of the servo signalare shown in Table 1.

TABLE 1 Thickness of magnetic layer Distance Output Defect Jitter (μm)(mm) (mv) (pieces) (μs) 0.13 0.3 200 15 34 0.13 0.5 180 16 35 0.13 0.7150 17 35 0.13 0.8 125 80 50 0.13 1 80 300 65 0.11 0.3 180 16 35 0.080.3 150 18 35 0.15 0.3 220 14 32 Standard value 100 or smaller 65 orsmaller

Now, items of the Table 1 will be respectively described below.

Distance: A distance between the magnetic tape and the permanent magnetswas shown.

Output: An output obtained by reproducing the servo signal by thereproducing head was read by an oscilloscope and the read output wastaken as an output.

Defect: the servo signal is reproduced by using an LTO-2 drive (Ultrium460 produced by HP). A part in which an output decreases by 25% from theaverage value of the peak of the reproduced servo signals was consideredto be a Defect and the average numbers per track in an entire lengthwere indicated.Jitter: the servo signal was reproduced by the same method as describedabove. S1 was obtained from the reproduced signal. S1 of 2048 frames wasobtained and a standard deviation therefrom was taken as Jitter.

S1 is defined as shown in FIG. 5. The evaluation of the Defect isdetermined by the evaluation standard of an LTO format.

As apparent from the Table 1, according to this Example, even when thethickness of the magnetic layer is decreased, the output and quality ofthe servo signal are good.

COMPARATIVE EXAMPLE

Then, the same pancake used in the above-described Example was used toAC erase. A coil was attached in place of the DC erasing magnet of aservo signal recording device to AC erase. A pancake in which thethickness of an upper layer is changed to a range of 0.08 to 0.18 μm wasprepared and the output of the servo signal and the quality of the servosignal were evaluated in the same manner as described above. The resultsthereof were shown in Table 2.

TABLE 2 Thickness of magnetic layer Output Defect Jitter (μm) (mv)(pieces) (μs) 0.18 220 11 34 0.15 150 14 35 0.13 110 285 58 0.1  80 30066 0.08 60 500 68 Standard value 100 or smaller 65 or smaller

It is recognized from the Table 2 that when the thickness of a magneticlayer is decreased, the output of the servo signal becomes low and thequality of the signal is deteriorated.

As described above, according to the present invention, since the servosignal can be recorded with the high reproduced output and the lowJitter, a highly accurate tracking operation can be carried out.Further, since the Defect is low, the highly accurate tracking operationcan be performed. According to the present invention, the track pitch ofthe magnetic recording medium can be reduced to increase its recordingdensity.

EXAMPLE 2

Now, an embodiment in which a DC erasing is performed by using amagnetic head in place of the above-described permanent magnets will bedescribed below by referring to FIGS. 6 and 7. In FIGS. 6 and 7, partsthe same as those of FIGS. 1 and 3 are designated by the same referencenumerals.

FIG. 6 shows a servo signal recording device according to thisembodiment and is a conceptual view of a device for recording a servosignal S on a magnetic tape T. In FIG. 6, reference numeral 11designates a recording head unit (servo signal recording means) in whicha magnetic head (a recording head) for recording the servo signal S isdisposed. Reference numeral 42 designates a servo part demagnetizingunit (DC erasing means) having a demagnetizing head disposed for erasinga servo signal part on the magnetic tape T before a recording operation.13 designates a reproducing head unit in which a magnetic head (areproducing head) for reproducing the servo signal S is disposed.

Further, the servo signal recording device has conveying means forlongitudinally conveying the magnetic tape T from a tape taking out part14 to a tape winding part 15.

The recording pattern of a magnetic recording medium in this embodimentis the same as that described in FIG. 2. Further, the structure of themagnetic recording medium, the thickness of a magnetic layer, thethickness of a non-magnetic layer, and the magnetic resistance of themagnetic tape are the same as those described in the above-describedembodiment.

FIG. 7 is a recording method in this embodiment. In FIG. 7, referencenumeral 51 designates a recording head in the recording head unit 11shown in FIG. 6. 52 designates a DC erasing head in the servo partdemagnetizing unit 42 shown in FIG. 6.

The DC erasing is firstly performed using a magnetic field in thedirection opposite to that of a magnetic field for recording the servosignal by using the DC erasing head 52. Then, the servo signal isrecorded by using the magnetic field in the opposite direction to thatof the DC erasing by the recording head 51.

An arrow mark 31 in FIG. 7 shows a conveying direction of the magnetictape T, an arrow mark 32 shows a DC magnetizing direction by DC erasingand an arrow mark 33 shows a magnetizing direction by recording,respectively.

As the above-described methods for DC erasing, heads for generating amagnetic field on a servo signal recording part may have any form. Forinstance, a thin film head having the same form as that of the servosignal recording head (51), a ring shaped head having a Gap only in theservo signal part or the like may be employed.

As for the structure of the thin film head, any of methods disclosed inJapanese Patent Application Laid-Open Nos. hei 10-124820, hei 10-172109and hei 9-282608 may be employed. The structure of a bulk type head madeof ferrite may be produced by a method disclosed in Japanese PatentApplication Laid-Open No. hei 7-37225.

As for the direction (polarity) of electric current supplied to thedemagnetizing head, it is important to retain on the tape the magneticfiled opposite to the magnetic field for recording the servo signal.When the magnetic field should be written in the same direction, thesignal would be hardly outputted. Since the output of the servo signalis greatly associated with the quality (Defect, Jitter) of the servosignal, the output of the servo signal is desirably located within arange of 80 to 180 mV. When the output of the servo signal is not higherthan 80 mV, a servo defect is too large so that the head cannot trace acorrect position. To control the output of the servo signal, theelectric current to be supplied to the DC erasing head 52 is changed, sothat the intensity of the magnetic filed remaining on the tape can becontrolled.

The servo signal is recorded as described above. Accordingly, themagnetizing direction (shown by the arrow mark 32) by DC erasing in anon-signal area is opposite to the magnetizing direction (shown by thearrow mark 33) by recording the signal in a signal recording area, asshown in FIG. 4A.

Therefore, a boundary area in which the magnetizing direction iscompletely inverted is formed. Thus, a leakage flux is more increasedthan that of a conventional method and a high reproduced output and ahigh S/N ratio can be obtained upon reproducing the servo signal asshown in FIG. 4B.

In a two-layer particulate type media of this example, on a base filmmade of polyester terephthalate, a non-magnetic layer composed ofα-Fe₂O₃ and polyurethane is formed, and a magnetic layer made of Co—Y—Feferromagnetic material and polyurethane is formed thereon as shown inFIG. 7.

Then, a coating material for a lower layer and a coating material for anupper layer obtained in the same manner as those of the above-describedExample 1 were prepared. The coating material for the upper layer wasfilled with a curing agent (Coronate L produced by Nippon PolyurethaneCo., Ltd.) of 4 parts by weight and the coating material for the lowerlayer was filled with a curing agent of 2 parts by weight. Then, twolayers were applied on the base film at the same time. After that, apancake with the width of 12.650 mm was obtained via processes ofcalendering, curing and cutting. The thickness of the magnetic layer ofthe Example was located within a range of 0.08 to 0.15 μm.

(Example of Recording of Servo Signal)

The magnetic tape wound in the form of the pancake previously undergoesan AC demagnetizing process. Two servo signal recording heads areprepared. One head is used for a demagnetizing process, that is, usedfor the DC erasing head 52 shown in FIG. 7 and the other head is usedfor a recording the servo signal, that is, used for the recording head51 shown in FIG. 7.

The electric current is constantly supplied to the demagnetizing head(52). The direction of supplying the electric current is opposite to thedirection of the electric current to the recording head 51. The electriccurrent to the recording head 51 is constantly set to 3.4 A under whichan output does not change even when the electric current of a certainvalue or more is supplied.

The electric current supplied to the DC erasing head 52, the output ofthe servo signal and the quality of the servo signal are shown in Table3.

TABLE 3 Thickness of Electric magnetic layer current Output DefectJitter (μm) (A) (mv) (pieces) (μs) 0.13 3.6 200 15 34 0.13 3.4 180 16 350.13 3.0 150 18 35 0.13 2.6 125 83 50 0.13 2.0 80 315 65 0.11 3.4 180 1636 0.08 3.4 150 17 35 0.15 3.4 220 14 32 Standard value 100 or smaller65 or smaller

Now, items of the Table 3 will be respectively described below.

Electric Current: An electric current supplied to the DC erasing head 52was shown.

Output: An output obtained by reproducing the servo signal by thereproducing head was read by an oscilloscope and the read output wastaken as an output.

Defect: The servo signal is reproduced by using an LTO-2 drive (Ultrium460 produced by HP). A part in which an output decreases by 25% from theaverage value of the peak of the reproduced servo signals was consideredto be a Defect and the average numbers per track in an entire lengthwere indicated.Jitter: The servo signal was reproduced by the same method as describedabove. S1 was obtained from the reproduced signal. S1 of 2048 frames wasobtained and a standard deviation therefrom was taken as Jitter.

S1 is defined as shown in FIG. 5. The evaluation of the Defect isdetermined by the evaluation standard of an LTO format.

As apparent from the Table 3, according to this Example, even when thethickness of the magnetic layer is decreased, the output and quality ofthe servo signal are good.

As the DC erasing head 52, a different head that is not the same as therecording head 51 may be used. In this case, the same servo signalrecording head may be used as the recording head 51 and the DC erasinghead 52 as described above. Thus, one magnetic head of the same kind asone servo signal recording head used in a conventional recording devicemay be added thereto, so that the structure of the device can besimplified.

EXAMPLE 3

Now, an embodiment in which the present invention is applied to anevaporated tape having a magnetic layer of Co, Ni or the like formed ona base by a vacuum evaporation method will be described below. Thepresent invention is not limited to a below-described Example and may beapplied to producing devices and producing methods disclosed, forinstance, in Japanese Patent Application Laid-Open Nos. 2003-296919,2003-85742, 2003-45018, 2003-6851, 2003-346329, 2002-367135 and2002-245611, and any of metallic thin film type magnetic recording mediahaving a medium structure.

Now, the present invention will be described on the basis of specificexperimental results. In a metallic thin film type magnetic recordingmedium of this Example, on a base film made of polyester terephthalate,a metallic thin film layer made of Co is formed, and a carbon protectivefilm layer is formed thereon as shown in FIG. 8.

Initially, a polyethylene terephthalate film having the thickness of 5.0μm as a non-magnetic supporter was coated with Co by an obliqueevaporation method by using a vacuum evaporation device to form aferromagnetic metal thin film having the thickness of 50 nm as amagnetic layer.

Then, on the ferromagnetic metal thin film, DC voltage of −1.5 kV wasapplied to the magnetic recording medium by a high frequency plasma ofthe mixed gas of ethylene and argon gas by using an electrode and themagnetic recording medium itself as an opposed electrode, and adischarging operation was carried out to form the carbon protective filmhaving the thickness of about 8 nm on the ferromagnetic metal thin film.

Then, on a surface of the polyethylene terephthalate film opposite to asurface on which the ferromagnetic metal thin film was formed, a backcoat layer (an illustration is omitted) having the thickness of 0.5 μmand made of carbon and a polyurethane resin was formed.

Then, the surface of the above-described protective film was exposed tothe high frequency plasma generated under the conditions of the pressureof argon gas of 150 Pa, the applied voltage of 100 W, the frequency of13.56 MHz for ten seconds.

Then, a material obtained by dissolving perfluoropolyether lubricanthaving a carboxyl group in a hexane solvent was applied to the carbonprotective film with an amount of application of 5 mg/cm² to obtain themagnetic recording medium.

Then, a pancake having the width of 12.650 mm was obtained via processesof a hot roll and cutting. The thickness of the magnetic layer of theExample was located within a range of 0.03 to 0.13 μm.

In FIG. 8, a DC erasing is performed and a servo signal is recorded inthe Example in the same manner as that shown in FIG. 3. The DC erasingis firstly performed using a magnetic field in the direction opposite tothat of a magnetic field for recording the servo signal by usingpermanent magnets 22 a to 22 c. Then, the servo signal is recorded byusing the magnetic field in the opposite direction to that of the DCerasing by a recording head 21.

(Example of Recording of Servo Signal)

As the permanent magnet for DC erasing, three Nd—Fe—B magnets having themagnetic resistance of 1038 kA/m and the residual magnetic flux densityof 1.375 T were used to direct the magnetic field opposite to that forrecording the servo signal to the magnetic tape. In this Example, an Spole was directed to the magnetic tape. A distance from the magnetictape, the output of the servo signal and the quality of the servo signalare shown in Table 4.

TABLE 4 Thickness of magnetic layer Hc Mrt Distance Output Defect Jitter(μm) (kA/m) (mA) (mm) (mv) (pieces) (μs) 0.10 133 30 0.3 205 12 33 0.10133 30 0.5 180 16 35 0.10 133 30 0.7 150 17 35 0.10 133 30 0.8 125 80 500.10 133 30 1.1 80 300 65 0.08 130 24 0.3 180 16 35 0.05 132 20 0.3 12018 35 0.13 133 40 0.3 230 14 32 Standard 100 or 65 or value smallersmaller

Now, items of the Table 4 will be respectively described below.

Magnetic resistance Hc and Mrt: VSM produced by Toei Industry Co., Ltd.was used to measure hysteresis in an applied magnetic field of 15 kOeand obtain Hc and Mr. Mr was converted to a value per unit area of 1 cm²and the value was considered to be Mrt (mA).Distance: A distance between the magnetic tape and the permanent magnetswas shown.Output: An output obtained by reproducing the servo signal by thereproducing head was read by an oscilloscope and the read output wastaken as an output.Defect: The servo signal is reproduced by using an LTO-2 drive (Ultrium460 produced by HP). A part in which an output decreases by 25% from theaverage value of the peak of the reproduced servo signals was consideredto be a Defect and the average numbers per track in an entire lengthwere indicated.Jitter: The servo signal was reproduced by the same method as describedabove. S1 was obtained from the reproduced signal. S1 of 2048 frames wasobtained and a standard deviation therefrom was taken as Jitter.

S1 is defined as shown in FIG. 5. The evaluation of the Defect isdetermined by the evaluation standard of an LTO format.

As apparent from the Table 4, according to this Example, even when thethickness of the magnetic layer is decreased, the output and quality ofthe servo signal are good.

COMPARATIVE EXAMPLE

Then, the same pancake used in the above-described Example was used toAC erase. A coil was attached in place of the DC erasing magnet of aservo signal recording device to AC erase. A pancake in which thethickness of an upper layer was changed to a range of 0.08 to 0.18 μmwas prepared and the output of the servo signal and the quality of theservo signal were evaluated in the same manner as described above. Theresults thereof are shown in Table 5.

TABLE 5 Thickness of magnetic layer Hc Mrt Output Defect Jitter (μm)(kA/m) (mA) (mv) (pieces) (μs) 0.18 133 70 220 11 34 0.15 133 55 150 1435 0.13 133 40 110 285 58 0.10 133 30 80 300 66 0.08 130 24 60 500 68Standard 100 or 65 or value smaller smaller

It is recognized from the Table 5 that when the thickness of a magneticlayer is decreased, the output of the servo signal becomes low and thequality of the signal is deteriorated.

The DC erasing may be performed not only to the servo signal recordingpart, but also to the data signal recording part.

While the invention has been described in accordance with certainpreferred embodiments thereof illustrated in the accompanying drawingsand described in the above description in detail, it should beunderstood by those ordinarily skilled in the art that the invention isnot limited to the embodiments, but various modifications, alternativeconstructions or equivalents can be implemented without departing fromthe scope and spirit of the present invention as set forth and definedby the appended claims.

1. A magnetic recording medium having a data signal recording part and aservo signal recording part on a magnetic layer, wherein a DC erasing isperformed to the servo signal recording part by a magnetic field in afirst direction, and then a servo signal is recorded in the signalrecording area of the servo signal recording part by a magnetic field ina second direction opposite to that of the first direction.
 2. Themagnetic recording medium according to claim 1, wherein the DC erasingis also performed to the data signal recording part.
 3. The magneticrecording medium according to claim 2, wherein a magnetic film on whichthe servo signal is recorded is made of a metallic thin film.
 4. Themagnetic recording medium according to claim 3, wherein the DC erasingis performed by magnetizing the magnetic layer by a DC magnetic field.5. The magnetic recording medium according to claim 2, wherein the DCerasing is performed by magnetizing the magnetic layer by a DC magneticfield.
 6. The magnetic recording medium according to claim 1, wherein amagnetic film on which the servo signal is recorded is made of ametallic thin film.
 7. The magnetic recording medium according to claim6, wherein the DC erasing is performed by magnetizing the magnetic layerby a DC magnetic field.
 8. The magnetic recording medium according toclaim 1, wherein the DC erasing is performed by magnetizing the magneticlayer by a DC magnetic field.
 9. The magnetic recording medium accordingto claim 1, wherein said magnetic recording medium comprises a magneticlayer and a non-magnetic layer, and wherein said magnetic layer has athickness of 0.03 μm to 0.13 μm.
 10. The magnetic recording mediumaccording to claim 9, wherein said non-magnetic layer has a thickness of0.5 μm to 2.5 μm.
 11. The magnetic recording medium according to claim9, wherein a magnetic resistance of the magnetic recording medium iswithin a range of 144 kA/m to 220 kA/m.
 12. The magnetic recordingmedium according to claim 1, wherein said first direction issubstantially opposite to the direction of travel of the magneticrecording medium.
 13. The magnetic recording medium according to claim12, wherein said second direction is substantially the same as thedirection of travel of the magnetic recording medium.